1. Lipids: Not Just Fat
BIOL 103, Chapter 6

2. Today’s Topics What are Lipids? Fatty Acids are Key Building Blocks
Triglycerides
Phospholipids
Sterols
Lipids Digestion and Absorption
Lipids in the Body
Lipids in the Diet
Lipids and Health

3. Lipids Essential nutrients Provide energy
Help transport fat-soluble nutrients
Contribute to flavor and texture of food

4. What are Lipids? Lipids include… Triglycerides (most abundant lipids)
In body: stored in adipose tissue
In food: “fats and oils”
Phospholipids (~2% of dietary lipids)
Plant and animal origin
Body can make them
Soluble in fat and water
Sterols (very, very small % of lipids)
Most well known: Cholesterol

5. Fatty Acids are Key Building Blocks
Determine whether a fat is solid or liquid at room temperature
Basic structure: (-COOH); (-CH3)
Chain length
2-24 Carbon length

6. Fatty Acids are Key Building Blocks
Saturation
Saturated fatty acids
All single bonds between carbons
Unsaturated fatty acids
One or more carbon bonds is a double bond
Monounsaturated fatty acid (MUFA)
Polyunsaturated fatty acid (PUFA)
Fats with more double bonds are generally more liquidy

7. Saturated vs. Unsaturated Fatty Acids

8. Fatty Acids are Key Building Blocks
Cis fatty acids
Trans fatty acids
Occurs naturally
Chain is bent
Produced by hydrogenation (adds hydrogen to an unsaturated fatty acids)
A small portion of trans fat can occur naturally
Chain is straighter

9. Trans Fat
In health, trans fatty acids are known to raise LDL (“bad”) cholesterol, and lower HDL (“good cholesterol”), promote systemic inflammation, and increase triglycerides in your blood.
History and how it is made:
In Europe (1910)
In US (1960s)

10. Fatty Acids are Key Building Blocks
Nonessential and essential fatty acids
Nonessential fatty acids
Can be made in the body
Not “essential” to have in your diet

11. Fatty Acids are Key Building Blocks
Nonessential and essential fatty acids (cont.)
Essential fatty acids
Can’t be made in the body
Must come from food
Omega-3 (alpha-linolenic acid) and omega 6 (linoleic acid)
Used to make eicosanoids

12. Triglycerides Structure Functions Glycerol + 3 Fatty Acids
Energy source: 9 kcal/g
Energy reserve: form of stored energy in adipose tissue (“fatty tissue”)
Insulation and protection:
Visceral fat (fat around organs)
Subcutaneous fat (fat under skin to protect/insulate body)
Carrier of fat-soluble nutrients
Sensory qualities in food

13. Apple vs. Pear

14. Triglycerides in Food Found in a variety of fats and oils
Classified by their most prevalent type
Saturated fatty acids: animal foods and tropical oils
Polyunsaturated fatty acids: plant or animal based
Omega-3: soybean, flaxseed oils; salmon, tuna
Omega-6: seeds, nuts, corn oil, meat, poultry, eggs

15. What are the positive and negative consequences of hydrogenating a fat
What are the positive and negative consequences of hydrogenating a fat? (Problem Set 6, #3)
Oxidation causes food to spoil and damage body tissues
Pros
Cons

16. Phospholipids Structure Functions:
Glycerol + 2 fatty acids + phosphate group
Functions:
Emulsifiers
Keep fat suspended in water
Keep oil and water mixed
Structural element for cell membranes

17. Phospholipids Cell membrane Double layer of phospholipids
Store fatty acids temporarily and release them as needed  can regulate them closely
Important role in nerve cells
e.g. Ach

18. Phospholipids Lipid transport Stomach Intestine Blood
Breaks fat into tiny particles for digestion (i.e. lingual lipase)
Intestine
Continues emulsifying fat (i.e. bile)
Blood
Coat the surface of the lipoproteins that carry lipid particles to their destinations in the body

19. Phospholipids Emulsifiers (Lecithin) In body In food
Phospholipid with choline  phosphotidylcholine
In food
Blend of phospholipids with different nitrogen-containing components
Used as emulsifiers (e.g. salad dressing, chili, sloppy-joe mixes, and chewing gum).

20. Phospholipids Phospholipids in food
Occur naturally in plants and animals
Examples: Egg yolks, liver, soybeans, peanuts
Not dietary essential because the body can make it

21. Sterols A category of lipids that include cholesterol
Structural characteristics:
Multiple ring structure
Contain no fatty acids
Unlike TAG and PL, Sterols do not have glycerol backbone and fingerlike FA structures

22. Sterols Cholesterol functions: Cholesterol synthesis in liver
Structural component of cell membranes
Precursor to other substances
Examples: Vitamin D, Sterol Hormones, Manufacture bile salts
Cholesterol synthesis in liver
Sterols in food
Found only in animal foods

23. Lipid Digestion
Digestion of triglycerides (TG), cholesterol, and phospholipids (PL)
Mouth
Chewing + lingual lipase
Stomach
30% Triglycerides + gastric lipase  FFA and DG

24. Lipid Digestion (cont.)
Small Intestine
Emulsified by bile
Rest of the “exposed” TG and DG are digested by pancreatic lipase
Phospholipids digested by pancreatic phospholipase
Cholesterol ester digested by cholesterol esterase
Bile salts surround digested fat and form micelles

25. Lipid Absorption

26. Lipid Digestion (cont.)
Micelles carry digested fat through the watery environment to microvilli/small intestine
The lipid components are then absorbed into the intestinal cells at the microvilli
Bile salts return to the liver to be used again
Short-chain FA and glycerol are directly absorbed into your intestinal cells without the help of micelles.

27. Lipids Absorption
To travel in the bloodstream, lipids are packaged into lipoprotein carriers
How?
In your intestinal cell: MG + FFA rejoin  TG
Cholesterol esters and phospholipids form here also
Then, TG, PL, cholesterol esters join protein carrier  lipoprotein.
Lipoprotein leaves the intestinal cell  chylomicron  goes to lymph system  bloodstream.

28. Lipid Digestion and Absorption (Figure 6.21)

29. Chylomicron Transport
In the blood stream, chylomicrons are large, fatty lipoproteins (90% fat)  circulate in the body while releasing TG
When reaching capillaries, lipoprotein lipase “attacks” chylomicrons to remove TG  FFA and glycerol:
FFA enter adipose cells  reassembled into TG
OR FFA enter muscle cells  used for energy
Glycerol  liver or kidney
Your liver picks up “left-over” chylomicron and uses them to build VLDL

30. Lipids in the Body Very-low-density lipoproteins (VLDL):
Deliver triglycerides to cells
Intermediate-density lipoproteins (IDL)
Returns to liver and is converted to LDL
Low-density lipoproteins (LDL)
Deliver cholesterol to cells, which body uses to synthesize membranes, hormones, etc.
Returns to liver afterwards
High-density lipoproteins (HDL)
Pick up cholesterol for removal or recycling

31. Lipoprotein Pathway Summary

32. Lipoprotein density
Lipoproteins differ by size, density, and composition of their lipid cores
In general, larger the lipoprotein, the less dense it is.
Size: HDL < LDL < IDL < VLDL < Chylomicron

33. Problem Set 6, Q#4:
Describe the differences between LDL and HDL and protein composition

34. Lipids in the Diet Recommended intake:
Reduce saturated fat and trans fat
Total fat: 20-35% of calories
Less than 10% of calories from saturated fat

35. Lipids in the Diet Essential FA requirements
Linoleic acid/omega-6 FA should provide about 2% of calories
Requirements for omega-3 FA is less well-known
Omega-6 and omega-3 FA balance
Ratio of 6:1 (omega-6 to omega-3 FA)
While omega-3 FA is good for you, consuming too much of the omega-3 FA can suppress immune function and prolong bleeding time

36. Lipids and Health
Following are examples are diseases associated to high intakes of saturated and trans fat.
Obesity
Determined by excessive accumulation of body fat leading to a body weight in relation to height that is significantly greater than some accepted standard.
High-fat diets promote weight gain
Heart Disease/Cardiovascular Disease
Leading cause of death in US (1 death/minute)
Major risk factors
High blood cholesterol (High LDL, low HDL)
Smoking
High blood pressure

37. Lipids and Health Atherosclerosis Inflammation and atherosclerosis
Slow, progressive hardening and narrowing of arteries
Promoted by high blood cholesterol
Inflammation and atherosclerosis
How?
Smoking, infection, or high blood pressure can speed up this process described above

38. Atherosclerosis

39. AHA diet and lifestyle recommendations:
Reducing heart disease risk (pg )
Go over on your own
Consume an overall healthy diet
Aim for a healthy body weight
Aim for a desirable lipid profile
Aim for normal blood pressure
Aim for normal blood glucose levels
Be physically active
Avoid use of and exposure to tobacco products
I have listed them, but go over on your own.
AHA: American Heart Association

40. AHA diet and lifestyle recommendations (cont.):
Reducing heart disease risk (pg )
Balance calorie intake and physical activity to achieve or maintain a healthy body weight
Consume a diet rich in fruits and vegetables
Choose whole-grain, high fiber foods
Consume fish, especially oily fish, at least 2/week
Limit your intake of saturated and trans fat

41. AHA diet and lifestyle recommendations (cont.):
Reducing heart disease risk (pg )
Minimize your intake of beverage foods with added sugars
Choose and prepare foods with little or no salt
If you consume alcohol, do so in moderation
Follow the AHA recommendations when eating outside of the home

42. Metabolic Syndrome ¼ US adults has metabolic syndrome
Has at least 3 of the following symptoms:
Excess abdominal fat
High blood glucose
High serum triglycerides
High blood pressure
Low HDL cholesterol

43. Putting it all together
Healthy People 2020 objectives target:
Reducing deaths from heart disease and stroke
Reducing the number of adults with high blood cholesterol levels

44. Cancer Stages of development:
Initiation: a mutation in cell’s genetics  abnormal cell
Promotion: when a chemical (e.g. carcinogen) encourages initiated cells to become active
Reversible stage
Progression: when promoted cells multiply and invade healthy tissues

45. Cancer (cont.) Dietary and lifestyle factors for reducing cancer risk:
Maintain a healthful weight
Adopt a physically active lifestyle
Consume a healthy diet
If you drink alcohol, limit consumption